The present invention relates to coated optical fibers comprising a novel combination of coatings, and more particularly to hermetically coated optical fibers incorporating high-intensity colored coatings and offering improved color coding characteristics.
Glass optical fibers provided with hermetic coatings are well known. Typically, the hermetic coatings are metallic or carbon-based coatings which act to protect the fiber from the potentially harmful effects of water vapor or gaseous contaminants affecting optical transmission characteristics or fiber strength. U.S. Pat. Nos. 4,407,561 (Wysocki) and 5,000,541 (DiMarcello et. al.) disclose examples of hermetically coated optical fibers, and many others are known.
In optical fiber cabling containing a multiplicity of optical fibers, it is often desirable to provide the individual fibers with coatings of various distinctive colors, as is done with copper telephone cabling, in order to be able to quickly differentiate the various fibers from each other. Optical fibers supporting colored coatings for this purpose are also well known, as shown, for example, by U.S. Pat. No. 4,629,285 (Carter et al.). That patent discloses optical fibers provided with colored ink coatings, with the preferred coatings being composed of pigmented opaque UV curable polymer inks.
Published European Application EP 411,310 (Mizutani) describes optical cables containing a plurality of color-coded optical fibers, and discloses optimum proportions of pigments to be added to the polymer fiber coatings in order to achieve adequate coloration while still insuring that the coatings are curable using ultra-violet light.
It has been appreciated that optical fibers comprising hermetic coatings, in particular carbonaceous hermetic coatings, are difficult to color-code in the conventional manner. Thus U. S. Pat. No. 5,074,643 (Petisce) recognizes that conventional hermetic coatings impart a dark coloration to the fiber surface which is hard to hide, and which therefore reduces the color intensity provided by conventional colored ink formulations. The solution proposed in that patent is therefore to utilize an organic opacifying agent in combination with a non-pigment colorant, ie., an organic dye compound. The patent suggests that such organic dyes can impart adequate coloration to the fiber when employed in a suitably opacified base coating.
While specifically addressing the difficulties associated with the color coding of hermetically coated optical fibers, the approach of this latter patent does involve some disadvantages. First, it cannot employ conventional colored polymer systems already successfully developed for the color coding of standard optical fibers, but instead requires a complete reformulation of those coatings for the special case of hermetically coated fibers. This then requires that two rather than a single set of color coating formulations must be kept in inventory to handle both normal and hermetically coated fiber production.
Additional concerns which must be addressed, for these organic dye coatings as well as any other new coating system which includes previously untested organic components, include the need to qualify the optical coatings for use in optical cables under a variety of different environmental conditions. Also to be considered are issues relating to the cost, availability, and stability of the organic dye compounds. Among the known difficulties with organic dyes are limited thermal and light stability, potential "bleeding" of the color into other cable components, possible interference with curing, and a susceptibility to fading on aging.
It is therefore a principal object of the present invention to provide a color coding method for optical fibers, and particularly for hermetically coated optical fibers, which solves many of the problems posed by prior art color coding methods.
It is a further object of the invention to provide an optical fiber coating system which facilitates the color coding of hermetically coated and other fiber types with relatively intense and easily differentiable colors.
It is a further object of the invention to provide a coated and color-coded optical fiber of novel configuration, and wherein the coating system employed does not adversely affect the optical properties of the fiber to which it is applied.
It is a further object of the invention to provide a coated and color-coded optical fiber of novel configuration.
Other objects and advantages of the invention will become apparent from the following description.